The command line length depends on the OS:

Windows NT, the command line is limited to 256 characters.
Windows 2000, the command line is limited to 2046 characters.
Windows XP, the command line is limited to 8190 characters.

For all OS's NTFS and FAT allows pathnames of up to 260 characters.

If you're not reaching any of these limits with your command line, then maybe telnet has it's own input limit. In which case you may want to break up your input line with a continuation character, which I think is "\" at the end of the line.

unix ,This is in the /usr/include/limits.h file
ex.the limit there is _POSIX_PATH_MAX = 255 per file name.
_POSIX_MAX_INPUT : Maximum number of bytes allowed in a terminal input queue. Value: 255

link : description for limits.h